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ECONOMIC IMPACT OF MODEL PREDICTIVE UNCERTAINTY ON TMDL ASSESSMENTS: A CASE STUDY IN THE LAKE ELSINORE SAN JACINTO WATERSHED
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.orgCitation: Watershed Management to Meet Water Quality Standards and Emerging TMDL (Total Maximum Daily Load) Proceedings of the Third Conference 5-9 March 2005 (Atlanta, Georgia USA) Publication Date 5 March 2005 701P0105.(doi:10.13031/2013.18060)
Authors: K. Bubb, T. Meixner
Keywords: Economic analysis, TMDL, Model, Sediment, Uncertainty
The economic and environmental consequences of over or underestimating model predictive
uncertainty in TMDL assessments are potentially significant. Current methods for arbitrarily
assigning a margin of safety (MOS) factor to model predictions are likely underestimating
uncertainty and misguiding regulators in the TMDL decision making process. In order to
investigate the economic impact of varying levels of assumed uncertainty, a hypothetical TMDL
for sediment load reduction in the San Jacinto Watershed was selected as a case study. Using the
Soil and Water Assessment Tools (SWAT) model, three different assumed amounts of
uncertainty, (1) an arbitrary 10% MOS factor, (2) model parameter uncertainty determined by
ParaSol, and (3) model predictive uncertainty determined by SUNGLASSES, were assigned to
model sediment load predictions. Cost estimates for extended detention basin (EDB)
implementation in the watershed were determined for three different TMDL goals based on
conservative, moderate, and liberal estimates of sediment loads into Canyon Lake.